The present invention relates generally to the metal treatment industry, and more particularly to clamps used to secure work holding racks to bus bars during such operations.
In anodizing and plating operations, metal parts are required to be immersed into tanks containing an electrolytic solution. The parts are first placed in a container or onto racks before being immersed into the electrolyte. The containers and racks are generally constructed of an electrically conductive material, such as, aluminum because the metal treatment operation necessitates the passing of an electric current through the parts to be treated and the electrolyte.
The containers and racks are typically hung from an electric current carrying bus bar positioned over the plating tank. The bus bar conducts a source of electrical current to the racks and through the parts to be treated and through the electrolyte and finally to a ground terminal.
Because the current in effect passes through the bus bar and into the work rack, it is essential there be a reliable electrical contact between the bus bar and the rack to insure no electrical losses occur. As should be apparent to those skilled in the art, the point of contact between the rack and the bus bar is called the rack arm. Various means have been employed to hold the rack arm to the bus bar such as by bolting the rack on to the bus bar, or by utilizing a cast iron or plastic "C" clamp, or by utilizing locking pliers.
Each of these types of devices have their respective advantages and disadvantages. The common disadvantage, of each of the above named tools, is that the use thereof is time consuming. Furthermore, tools such as locking pliers are expensive.
One tool, the woodworker's steel spring clamp, is both quickly utilized during metal treating operations and inexpensive to manufacture. This is a tool characterized by a pair of steel hand grips or tongs and a spring which forces the steel tongs into closure. The typical woodworker's clamp is essentially comprised of four (4) main parts: two juxtaposed arms or tongs, a spring which forces the holding ends of the arms together in a clamping action, and a tubular rivet which holds the two arms in a pivoted relationship.
During plating and anodizing operations, the bus bars become corroded through contact with the electrolyte solution splash. In addition, the rack arms distorted, corroded and oxidized. In these instances, the optimum ideal situation of a clean bus bar and flat conductive surface joined intimately by a clamping device is not present. Experience with the use of woodworker's spring clamps in such operations under the aforementioned conditions wherein the contact between the rack arms and the bus bar is marginal has shown that a disproportionate part of the incoming current passing through the bus bar is oftentimes diverted up through the clamp following the path of least resistance rather than down the rack arm and into the work load in the tank. This occurs probably because one of the pressured spring ends makes positive contact with the back side of the bus bar. When this occurs the high current passing through the clamp and into the coil causes it to become in effect a glow coil, heating up to a cherry red to orange color equivalent to approximately 1300 to 1600 degrees Fahrenheit. The spring immediately loses physical properties and the clamp has no holding power, becomes non-functional and is usually discarded.
The present invention is designed to overcome the above noted limitations that are attendant upon the use of prior art clamping and securing devices of the metal treatment industry, and toward this end, it contemplates the provision of a novel clamping device for assuring positive electrical contact between rack arm and the electrical current carrying bus bar during a metal treatment operation.
It is an object of the invention to provide such a clamping device which can be easily and efficiently used during such an operation with increased reliability.
Still another object is to provide such a device which prevents shunting of electrical current through the coil spring thereby eliminating undesirable heating and failure thereof.
A further object is to provide such a device which may be readily and economically fabricated and will enjoy a long life in operation.